Abstract:
This is a parent metadata record for work carried out as part of ASAC/AAS project 40.

See the child metadata records for further information.

More than 95% of the biomass in the Southern Ocean is microscopic - single celled plants, animals, bacteria and viruses. We are studying the factors that control their distribution and abundance - oceanographic and seasonal conditions, their physiology, ... and grazing - in order to model their vital roles as food for other organisms and their influence in moderating global climate change through absorption of CO2 and production of DMS. We are also addressing the changes expected in microbial communities through effects of climate change - global warming, sea ice retreat, ocean acidification and enhanced ultraviolet radiation.

This project aims to determine the role of microorganisms in the Southern Ocean. The major objectives are to:

* Identify and quantify key protistan components of the Southern Ocean ecosystem and study their autoecology.

* Identify environmental and ecological processes that control abundance of key microbial components.

* Determine the activity and viability of bacterioplankton and protists in the Southern Ocean.

* Distinguish different microbial communities by identifying key taxa and associations so that processes such as primary production, respiration, grazing and particle flux can be readily parameterised in ecological models.

* Determine the effect of elevated CO2 concentrations on microbial populations and processes.

Taken from the 2008-2009 Progress Report: Progress against objectives: 1. Ongoing sampling from Astrolabe has continued, with 3 return voyages being sampled for phytoplankton species, chlorophyll a and other pigments, coccolithophorid counts and DNA profiles, in conjunction with measurements of CO2, ocean structure, fluorescence and ocean colour by CSIRO / CRC colleagues.

2. Three sets of minicosm experiments were conducted at Davis station with 7 staff spending 4.5 - 5.5 months on site. These experiments consistently found that acidification caused blooms of nanoplanktonic diatoms and increased bacterial activity, apparently by inhibition of microheterotroph grazers, at the expense of larger cells that are more readily ingested by grazers such as krill. We showed for the first time in Antarctic waters that pCO2 affects the structure and function Antarctic microbial communities in a way that may reduce food availability to large grazers. Over 100 cultures of "winners and losers" from such experiments were isolated and returned to Australia. These will form the basis for further physiological experiments including molecular assays.

3. Submission and acceptance of 8 papers from the BROKE-West cruise (5 as senior author). These showed the interactions between bottom-up (micronutient) top-down (grazing) control in structuring microbial populations in the marginal ice zone. Five biogeographic zones were identified on the basis of species composition, and the productivity was measured for each zone. Microzooplankton grazing experiments found that grazing within that microbial loop consumed a significant proportion of new productivity. In some areas later in the season, all productivity was consumed by microheterotrophs, rather than metazoans such as krill. A time sequence was identified for seeding and development of components of ice edge blooms, subsequent grazing and decline and a mechanism postulated for export of micronutrients (e.g. iron) by grazing and sedimentation that prevents subsequent development of surface water blooms and constrains populations to a deep chlorophyll maximum below the level of a nutricline.

4. Detailed analysis of greater than 30 strains of keystone species Emiliania huxleyi of two morphotypes in conjunction with Clara Hoppe (Masters student, Alfred Wegener Institute) and Suellen Cook (PhD student, University of Tasmania) showed consistent differences between strains in terms of pigmentation, responses to light and genetics. The two morphotypes appear to be adapted to different mixing regimes north and south of the Polar Front; the southern form may represent a new species.

For a full list of references associated with this project, see the project link at the provided URL.